1. Field of the Invention
The present invention relates to improved endodontic instruments and the manufacture of such instruments by grinding a wire stock.
2. Description of the Prior Art
Endodontic instruments commonly referred to as files are utilized by dentists for cleaning and enlarging the root canals of human teeth. The purpose of the cleaning and enlarging procedure is to remove infected tissue from the root canals and enlarging the root canals so that they can be filled. A commonly used such endodontic instrument is known as a K-type file which has a tapered shaft including three or four spiral flutes along the length thereof. A preferred form of K-file includes three flutes, the cross-sectional shape of the shaft is triangular and the flutes form three spiral cutting edges along the length of the tapered portion of the shaft. Another type of endodontic instrument, known as a reamer, has three or four spiral flutes forming three or four spiral cutting edges thereon. These and other endodontic instruments are manufactured in accordance with standards set up by the American Dental Association and other standardizing bodies.
A problem which is often experienced by dentists in using endodontic instruments like those described above involves the self-feeding or threading of the endodontic instruments into the root canals being enlarged which often causes the instruments to break off in the canals. Another problem associated with the heretofore used endodontic instruments is the requirement that a number of different size instruments having different uniform tapers must be used for each root canal preparation. That is, the dentist must use numerous instruments with different uniform tapers to complete each root canal preparation prior to filling the canal with gutta percha. Thus, there are needs for improved endodontic instruments which do not self-feed into the root canal and which do not require the use of multiple uniform taper instruments.
Various machining processes and apparatus for producing endodontic instruments have been developed and utilized, a particularly suitable process and apparatus are described in U.S. Pat. No. 4,999,952 dated Mar. 19, 1991 and U.S. Pat. No. 5,065,549 dated Nov. 19, 1991, both to Speiser et al., and both of which are incorporated herein and made a part hereof by reference thereto.
While the machining process disclosed in the above mentioned patents to Speiser et al. have been used successfully for the manufacture of endodontic instruments of the types described above, there is a continuing need for improvements to such process whereby improved endodontic instruments can be produced thereby.
The present invention provides improved endodontic instruments and an improved machining process for manufacturing the instruments which meet the needs described above and overcome the deficiencies of the prior art.
An improved endodontic instrument of this invention adapted for use in performing root canal therapy is basically comprised of an elongate shank having a proximate end, a pilot end and a tapered peripheral surface adjacent the pilot end thereof. A first plurality of continuous helical flutes which form cutting edges on the peripheral surface are formed in and extend along a first portion of the peripheral surface. A second plurality of continuous helical flutes which form cutting edges on the peripheral surface are formed in and extend along a second portion of the peripheral surface adjacent to the first portion thereof. The second plurality of helical flutes contains a number of flutes different from the number of flutes in the first plurality of helical flutes. As a result of the different number of flutes in the pluralities of continuous helical flutes on the peripheral surface of the instrument, the instrument is prevented from self-feeding in a root canal when being used. The endodontic instrument can include additional pluralities of continuous helical flutes which form cutting edges on the peripheral surface formed in and extending along third and additional portions of the peripheral surface, each of the additional pluralities of helical flutes containing a number of flutes different from the number of flutes in adjacent pluralities of helical flutes.
The improved process of this invention for producing the above described endodontic instrument, i.e., an instrument which includes successive pluralities of continuous helical flutes containing different numbers of flutes, which does not self-feed in a root canal basically comprises the following steps. A first grinding wheel rotated about a first axis is provided having a plurality of flute grinding ribs and an extra flute grinding rib extending from a periphery thereof. A rotating wire stock is fed past the plurality of flute grinding ribs and the extra flute grinding rib along a second axis at a first feed rate and rotation rate such that a separate spiral flute is ground on the wire stock by each of the plurality of flute grinding ribs and by the extra grinding rib. The feed rate and rotation rate of the wire stock past the plurality of flute grinding ribs and the extra flute grinding rib are increased so that a separate spiral flute is ground on the wire stock by each of the plurality of flute grinding ribs and the extra flute grinding rib follows the spiral path of the first flute grinding rib to make grinding contact with the wire stock. Optionally, the first feed rate and rotation rate or both the first feed rate and rotation rate and the increased feed rate and rotation rate can be repeated to form one or more additional pluralities of continuous flutes on the instrument. Simultaneously with the grinding of the flutes, the grinding wheel or the wire stock is translated, i.e., moved, such that a distance between the first and second axes increases as the wire stock is fed whereby a single pass of the wire stock past the flute grinding ribs and the rolled deformed metal grinding rib produces a tapered multi-fluted endodontic instrument.
A preferred process of this invention includes the above steps in combination with the following additional steps. First and second tapered grinding surfaces are provided on the grinding wheel for forming a desired form of tip, such as a tapered tip, on the rotating wire stock, and for parting a previously formed multi-fluted tapered endodontic instrument from the rotating wire stock. In addition, a second grinding wheel having a plurality of depth indicating calibration grinding ribs extending from a periphery thereof which is rotated about a third axis is provided. The first grinding wheel is retracted from a flute grinding position with the rotating wire stock to a non-grinding position, and the rotating wire stock is fed forward a predetermined distance. Thereafter, the feed of the rotating wire stock is temporarily terminated while the first and second grinding wheels are advanced into grinding contact with the wire stock whereby a previously formed tapered multi-fluted endodontic instrument is parted from the wire stock, a tip having a desired form is ground on the wire stock and depth indicating calibration grooves are ground on the wire stock. The first and second grinding wheels are retracted whereby the first grinding wheel is returned to the flute grinding position and the second grinding wheel is returned to a position out of contact with the wire stock. The feed of the rotating wire stock is then resumed so that the proper taper and flutes are ground on the wire stock whereupon the above steps are repeated.
Another improved endodontic instrument provided by this invention and produced by the above described process has two or more portions of the fluted tapered peripheral surface thereof of differing taper.
It is, therefore, a general object of the present invention to provide improved endodontic instruments and a process for forming the instruments.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.